Deep Coring

Deep Ice Sheet Coring (DISC) Drill

DISC Drill at WAIS Divide «

The DISC Drill is a tethered mechanical drill system capable of cutting and retrieving cores of ice to depths of 3,800 meters. The cores produced by the drill are approximately 12.2 cm (4.8 inches) in diameter and up to 4-meters long. Because of the great depths, the drill is designed to operate in a drilling fluid which provides the hydrostatic compensation necessary to prevent closure of the borehole due to the "glaciostatic" pressure of the surrounding ice. The drill system consists of several major subsystems:

Drill Sonde

The sonde is the down-hole portion of the drill system that actually cuts the ice. It consists of a cutting head, a core barrel in which the core is collected, a motor and transmission to drive the cutting head, a pump to circulate ice cuttings in the drill fluid through the sonde, screens to remove the ice chips from the fluid, an instrumentation/control section, and an upper section that contains anti-torques to stabilize the drill in the borehole and the mechanical, electrical power, and optic fiber terminations of the cable which include rotary joints that allow the drill sonde to rotate relative to the cable.

» Drill Sonde Being Assembled

Drill Cable

Cross Section of Drill Cable «

The cable is used to suspend the drill sonde in the borehole and to provide conduits for electrical power for the sonde and for communications between the sonde and the surface.

Tower

The tower is a mast at the top of the borehole with a number of pulleys to allow the raising and lowing of the sonde and positioning the sonde for removal of the core.  The DISC Drill tower tilts from vertical to horizontal to allow easy core removal and drill sonde servicing.

» Tower

Winch

Winch «

The winch provides the means of hoisting the drill from the hole. It is electrically driven and unusual in that the drum axis is parallel to the drill cable as the cable runs between the winch and tower with the level wind traversing back and forth across the width of the drum in line with the cable.  This configuration allows the winch to be connected to the tower base resulting in a smaller footprint.

Control System

Control for the entire drill system is PC based with the user interface being developed using LabView.  Data from the drill sonde, the tower, and the winch are displayed and drill control parameters set using the computers.  The computers are installed in a 1.78 meter x 3.53.meter x 2.00 meter insulated and temperature controlled room which is positioned to allow the operators to observe the drilling equipment and operations.

» Control Screens

Core Handling

Core Barrel Being Lowered Onto Core Transfer Table «

Because of the layout of the drill equipment and the core handling process developed by National Ice Core Laboratory (NICL), the core barrel must be rotated 180° before the core is pushed out of the barrel into the core processing ice tray.  Once the core barrel is disconnected from the rest of the sonde, it is lifted and rotated using a specially designed lifting device attached to a 2-ton gantry crane.  The barrel is then lowered onto a table and the core is pushed from the barrel onto a tray on a core processing table.

Drill Fluid and Fluid Handling

The first project utilizing the DISC Drill will use a two-part fluid similar to that used by the European deep coring projects. The heart of the fluid handling system is a tank in which the two drill fluid components are mixed.  All associated measurement devices, valves and pumps are integrated into the tank assembly and the mixing is controlled by a microprocessor.  The remainder of the system consists of piping to transport the fluids to the tank for mixing and piping to inject the mixture into the borehole.  Fluid that drips from equipment and that is recovered from the ice chips is returned to the borehole.  A centrifuge is used to remove fluid entrained in the recovered ice chips; the fluid is returned to the fluid system.

» Fluid Mixing Tank

Screen Cleaning

Screen Cleaning Station «

Screen cleaning equipment includes a station where the screens are removed from the housing and the individual screen sections cleared of ice chips.  The screen sections are reinserted into the housing at the screen cleaning station.  The screen cleaning station is semi-automated.  The chips are collected in a bucket that is inserted into the centrifuge for the removal of fluid from the chips.

Ancillary Equipment

Equipment not directly involved with the drilling operation, but integral to the system, includes a shop facility and a gantry crane.  The shop, designed to facilitate repairs to the drill in the field,  is contained in an expandable container shelter housing a machine shop, a welding shop, and an electronics shop. The A-frame gantry crane runs on rails that are used by the smaller core handling crane and is used to move equipment, particularly during drill system installation and “tear-down.”

» Shop

Safety Equipment

Air Monitor «

Safety equipment includes a multi-port gas monitor used to ascertain that areas with higher concentrations of drill fluid do not have dangerously high levels of vapors.  Fire extinguishers, personal safety equipment, and proper signage and alarms are also provided.

Field Tested

ICDS field tested the drill in Greenland during the summer of 2006.  First use of the drill for a science project was at WAIS Divide beginning in the 2007-2008 Antarctic field season.